Asexual propagation of plants has been shown for some species to yield large numbers of genetically identical embryos, each having a capacity to develop into a normal plant. Such embryos are usually further cultured under laboratory conditions until they reach an autotrophic “seedling” state characterized by an ability to produce its own food via photosynthesis, resist desiccation, produce roots able to penetrate soil, and fend off soil microorganisms. Some researchers have experimented with the production of artificial seeds, known as manufactured seeds, in which individual plant somatic or zygotic embryos are encapsulated in a seed coat. Examples of such manufactured seeds are disclosed in U.S. Pat. No. 5,701,699, issued to Carlson et al., the disclosure of which is hereby expressly incorporated by reference.
Typical manufactured seeds include a seed shell, synthetic gametophyte and a plant embryo. A manufactured seed that does not include the plant embryo is known in the art as a “seed blank.” The seed blank typically is a cylindrical capsule having a closed end and an open end. The synthetic gametophyte is placed within the seed shell to substantially fill the interior of the seed shell. A longitudinally extending hard porous insert, known as a cotyledon restraint, may be centrally located within one end of the seed shell, surrounded by the synthetic gametophyte, and includes a centrally located cavity extending partially through the length of the cotyledon restraint.
The cavity is sized to receive the plant embryo therein. The well-known plant embryo includes a radicle end and a cotyledon end. The plant embryo is deposited within the cavity of the cotyledon restraint, cotyledon end first. The plant embryo is then sealed within the seed blank by at least one end seal. There is a weakened spot in the end seal to allow the radicle end of the plant embryo to penetrate the end seal.
After a relatively large number of manufactured seeds are assembled, they are sowed in a nursery bed. As such, they are allowed to germinate with the anticipation of yielding a large number of healthy seedlings having desired characteristics. Although currently available manufactured seeds are relatively successful in yielding a reasonable number of healthy seedlings, such manufactured seeds are not without problems.
As an example, research has shown that embryo quality can reduce the germination of manufactured seeds. As a non-limiting example, with one set of embryos, germination was 50%. This can be improved by various sorting methods. As a result, as measured against the successful yield rate, the cost of manufactured seeds with low quality embryos is proportionately higher when evaluated against crop yield.
Thus, there exists a need for a multi-embryo manufactured seed that produces a higher successful yield rate than those currently available in the art.